During the life of a surface controlled subsurface well safety valve it may become necessary to lock the valve in the open position. Typically, this is done by conventional wireline methods. However, a hydraulic lock-out mechanism can be utilized as disclosed in U.S. Pat. Nos. 4,273,194 and 4,796,705 when wireline methods are not used. The hydraulic lock-out is performed by applying hydraulic pressure to a dedicated control line from the surface which actuates a lock-out piston and cylinder assembly with a locking mechanism. Once the subsurface valve has been locked out, the lock-out is permanent until the valve is pulled from the well and redressed. In the case of a tubing retrievable subsurface safety valve, this requires pulling the well production string which is time-consuming and expensive.
However, there are instances when it would be desirable to hydraulically lock out a safety valve and hydraulically return the valve back into operation from the surface. Also, there is the possibility in hydraulically locked open safety valves that the lock-out line can be inadvertently actuated which would permanently lock open the safety valve and in that case it would also be desirable to hydraulically reactivate the valve. The present invention is directed to a surface controlled subsurface well safety valve which may be hydraulically locked open from the surface when desired, but which can also be hydraulically returned to normal operation.